Cindy Harnett

Model based design of a microfluidic mixer driven by induced charge electroosmosis

Mixing chemical or biological samples with reagents for chemical analysis is one of the most time consuming operations on microfluidic platforms. This is primarily due to the low rate of diffusive transport in liquid systems. Additionally, much research has focused on detection, rather than sample preparation. In response, we describe a mixer for microfluidic sample preparation based on the electrokinetic phenomenon of induced-charge-electroosmosis (ICEO). ICEO creates microvortices within a fluidic channel by application of alternating current (AC) electric fields. The microvortices are driven by electrostatic forces acting on the ionic charge induced by the field near polarizable materials. By enabling mixing to be turned on or off within a channel of fixed volume, these electronically controlled mixers prevent sample dilution-a common problem with other strategies. A three-dimensional model based on the finite volume method was developed to calculate the electric field, fluid flow, and mass transport in a multi-species liquid. After preliminary experiments, the model was used to rapidly prototype a wide range of designs. A new microfabrication process was developed for devices with vertical sidewalls having conductive metal coatings and embedded electrodes. Mixing experiments were carried out in the devices and the results were compared to the model.

A review of electricity monitoring and feedback systems

This paper reviews various products available in market and under study, which monitor electricity consumption and provide feedback of the energy usage. Energy usage feedback systems are categorized into three groups: (i) socket monitoring systems, (ii) whole-house monitoring systems, and (iii) whole-house monitoring with breakdown to individual appliances. In the future directions section, the paper describes a proposed energy usage feedback system, which provides feedback about individual appliances. This system also considers the effect of human behavior on energy usage and suggests a possible solution.

Calibration and Field Deployment of Low-Cost Fluid Flow-Rate Sensors Using a Wireless Network

Low-cost networked fluid flow velocity sensors are needed for high-density sampling in environmental research and other applications requiring automated fluid flow velocity mapping. The flow sensor in this paper is the “target” type consisting of a flap that deflects in the flow, changing the resistance of a strain gauge. A highly compliant flexible resistor promises to reduce costs by serving as the flow target and by eliminating the signal amplification circuitry needed for conventional strain gauges. However, we show that the individual calibration of these resistive sensors is critical for recovering the stream flow velocity. A wireless network is used for the mass calibration of multiple sensors in a test flume. After individual sensor calibrations are obtained, the same wireless network can be used to collect flow velocity data in the sensor application. A modular connection system enables the user to reconfigure quickly the systems physical layout for calibration or deployment purposes. The results are reported on an outdoor deployment of the flow sensors for logging stream flow data in environmental research.

EMF Signature for Appliance Classification

Various intrusive and nonintrusive appliance load monitoring and classification systems have been studied; however, most of them designed so far provide group-level energy usage feedback. We present the first phase of a system with the potential to attribute energy-related events to an individual occupant of a space and provide occupant-specific energy usage feedback in an uninstrumented space (e.g., home or office). This initial phase focuses on collecting the electromagnetic field (EMF) radiated by several common appliances to determine a unique signature for each appliance. It also implements a machine learning algorithm to classify appliances from an incoming EMF data file. The proposed approach has been prototyped with hardware realization. The results obtained on tested appliances indicate the EMF sensors ability and potential to develop a system for providing occupant-specific energy feedback.

Modeling Human Behavior for Energy-Usage Prediction

We propose a system that uses a set of mobile sensors to model human behavior of energy usage. This mobile sensor suite can be fit on a keychain or ID/access badge. Data from these sensors, e.g., temperature, visible light spectrum, and 60 Hz electromagnetic field, will be used to give real-time feedback of user’s energy consumption and prediction of future energy usage. Feedback of energy consumption will be displayed in an understandable manner on a user interface, e.g., smart phone. A model developed from the available data using machine learning will inform the system about energy consumption patterns and behaviors of users.

Determining the Physical Sequence of Sensors on a Serial Bus With Minimal Wiring

This report demonstrates a three-wire system for determining the physical sequence of addressable devices on a serial bus, enabling automated spatial mapping of sensors along a network. Small inductors between each chip are incorporated into an oscillator circuit, producing a different resonant frequency for each chip during the sequence detect function. Frequency-counting-based sequence detection is compatible with small microcontrollers such as those used in wireless environmental sensor networks. The sequence detection hardware does not interfere with normal use of the same three wires to supply power, data, and ground connections to the wired sensor network in this application.

Bistable out-of-plane stress-mismatched thermally actuated bilayer devices with large deflection

In this paper, we explore microfabricated bistable actuators released as thin films from a silicon wafer. The actuators are based on a serpentine design where two cantilevers are coupled at the tips by a thin-film bar. These devices are parameterized by two lengths: cantilever length and the length of the coupling bar. These two dimensions are systematically varied to study the effect of design parameters on bistability. The three-dimensional devices have extremely large deflection (hundreds of microns rather than tens of microns for most planar microactuators of similar size) and are thermally actuated out of the plane of the wafer by applying a bias across either the left or right side of the serpentine. The bistability of these devices is evaluated using electron and optical microscopy. Potential applications include non-volatile mechanical memory, optical shutters, and reconfigurable antenna elements.

Wavelength specific excitation of gold nanoparticle thin-films

Advances in microelectromechanical systems (MEMS) continue to empower researchers with the ability to sense and actuate at the micro scale. Thermally driven MEMS components are often used for their rapid response and ability to apply relatively high forces. However, thermally driven MEMS often have high power consumption and require physical wiring to the device. This work demonstrates a basis for designing light-powered MEMS with a wavelength specific response. This is accomplished by patterning surface regions with a thin film containing gold nanoparticles that are tuned to have an absorption peak at a particular wavelength. The heating behavior of these patterned surfaces is selected by the wavelength of laser directed at the sample. This method also eliminates the need for wires to power a device. The results demonstrate that gold nanoparticle films are effective wavelength-selective absorbers. This “hybrid” of infrared absorbent gold nanoparticles and MEMS fabrication technology has potential applications in light-actuated switches and other mechanical structures that must bend at specific regions. Deposition methods and surface chemistry will be integrated with three-dimensional MEMS structures in the next phase of this work. The long-term goal of this project is a system of light-powered microactuators for exploring cellular responses to mechanical stimuli, increasing our fundamental understanding of tissue response to everyday mechanical stresses at the molecular level.

Control of electrolysis-generated microbubbles for sensor surface passivation

This letter outlines our work in generating and controlling microbubbles as protective “lids” for samples collected from the environment. The fabrication method uses “strain architecture” to construct three-dimensional cages with high surface area. These structures confine the bubbles and perform as electrodes for electrochemical sample collection and electrolysis-based gas bubble generation. The focus of this article is on the interaction between the microcages and generated bubbles, including the bubble generation mechanism, bubble growth rate, response to hydrostatic pressure, effect of interfacial-tension modifying coatings, and long-term stability.

Estimating Suspended Sediment Concentration in Streams by Diffuse Light Attenuation

AbstractA light attenuation sensor system (LASS) for measurements in waters is described in this paper. The LASS records irradiance at multiple levels in the water column to provide a measure of the diffuse light attenuation coefficient which is strongly affected by suspended sediment. Dimensional analysis and geometric optical theory are used to relate the irradiance attenuation to sediment properties through a dimensionless product. The latter is termed as a light attenuation number for suspended sediment in waters. The LASS and dimensional analysis results are validated in the laboratory using fluvial sediments collected from a third-order stream and monodisperse quartz sediment. The attenuation coefficient estimated with LASS data varied nonlinearly with total suspended sediment concentration due to particle shadowing and multiple scattering at large optical depths. The light attenuation coefficient for each sediment type is well described as a function of total suspended sediment concentration by emp...